The specifications of long-term evolution (LTE) have been developed for the purpose of achieving increased speed, lower delay and so on in UMTS (Universal Mobile Telecommunications System) (non-patent literature 1). In LTE, a communication scheme that is based on OFDMA (Orthogonal Frequency Division Multiple Access) is used in downlink channels (downlink), and a communication scheme that is based on SC-FDMA (Single Carrier Frequency Division Multiple Access) is used in uplink channels (uplink).
Successor standards of LTE (referred to as “LTE-advanced” (“LTE-A”) and so on) are under study for the purpose of achieving further broadbandization and increased speed. LTE-A is planned to employ a new transmission scheme such as multiple-user MIMO (MU-MIMO), which transmits information from different transmitting antennas to different user terminals, simultaneously.
When a new transmission scheme such as the above one is employed, there is a threat that the capacity of the downlink control channel (PDCCH: Physical Downlink Control CHannel) to transmit downlink control information (DCI) runs short and the characteristics of the LTE-A system cannot be optimized. So, in LTE-A, a study is in progress to employ a new radio resource structure that expands the radio resource region for DCI.